Vertical combustion test chambers are specialized flame retardant performance test equipment used to evaluate the combustion characteristics of materials in the vertical direction. Its core function is to fix the specimen vertically in the closed combustion box, apply a standard test flame under specified conditions, and evaluate the flame retardant performance of the material by measuring the flame combustion time, flameless combustion time, combustion length of the specimen, and whether the combustion droplets ignite the underlying bedding. This equipment is mainly used to evaluate the self-extinguishing ability and flame spread characteristics of materials when exposed to fire in the vertical use state, and is an essential testing instrument in the fields of electrical and electronic products, automotive interior parts, building materials and polymer materials.
Principle
The working principle of the vertical combustion test chamber is based on simulating the combustion behavior of the material after controlled ignition in the vertical direction. The equipment eliminates external airflow interference by establishing a standardized test environment in a closed box, so that the test results have good reproducibility. Its work process mainly includes the following key links:
The specimen is clamped vertically on a special specimen rack, the lower end of the specimen is located at the specified height, and a layer of cotton wool is placed below to receive possible combustion droplets. The Bunsen lamp is placed at a defined angle, usually vertically or at a specific angle to the specimen plane, with its tip at a standard distance from the lower edge of the specimen. The test uses a specified gas source (such as methane, propane or natural gas) to adjust the gas flow and pressure through a precision gas control system to stabilize the flame height and heat output power (usually 50W or 500W) within the standard requirements. The test procedure usually includes two flames, each flame time is fixed at 10 seconds, the afterflame time is recorded after the first flame, the second flame is carried out immediately after the flame is extinguished, and the afterflame time and afterglow time after the second flame are recorded, and the burning droplets are observed and recorded whether the lower cotton pad is ignited.
Key measurement methods and parameters
The measurement method of vertical combustion test is mainly based on UL 94, GB/T 2408, IEC 60695-11-10 and other standards, through the statistical evaluation of the test data of the specified number of samples.
1. Standard Test Procedures:The test usually uses a group of 5 specimens, and the specimens need to be adjusted to a specified state (such as 23°C, 50% relative humidity environment adjustment or 70°C high-temperature aging treatment). The specimen is clamped vertically, the upper end is about 6mm long, and the lower end of the specimen is 300mm±10mm away from the horizontally laid cotton layer. Adjust the flame height of the Bunsen lamp to 20mm±2mm, and the flame temperature must meet the standard requirements.
2. Timing Measurement:During the test, a number of time parameters need to be accurately recorded: the flame burning time t₁ after 10 seconds of the first flame; the flame burning time t₂ after 10 seconds of the second flame; Flameless burning time after the second flame (scorching burn time). Timing accuracy is usually required to be 0.1 or 0.5 seconds.
3. Drip Observation:During the test, it is necessary to observe whether the sample produces burning droplets and whether the droplets ignite the underlying cotton layer. This is the core criterion that distinguishes V-1 from V-2 grades.
4. Flame Spread Judgment:Observe whether the specimen burns or spreads to the grip of the fixture, that is, whether the specimen is completely burned.
5. Result evaluation formula:Based on the recorded time parameters, the material is graded by:
For V-0 levels: the flame burn time of each specimen is ≤ 10 seconds after each flame; The sum of the flame burning time of each group of 5 specimens after two flames is ≤ 50 seconds; The flameless burning time of each specimen after the second flame is ≤ 30 seconds; Do not allow combustion to spread to the fixture; Do not allow dripping objects to ignite the cotton pads.
For V-1 level: the flame burn time of each specimen is ≤ 30 seconds after each flame; The total flame burning time of each group of 5 specimens after two flames is ≤ 250 seconds; The flameless burning time of each specimen after the second flame is ≤ 60 seconds; Do not allow combustion to spread to the fixture; Do not allow dripping objects to ignite the cotton pads.
For V-2 levels: ≤ 30 seconds of flame burning time after each flame is applied to each specimen; The total flame burning time of each group of 5 specimens after two flames is ≤ 250 seconds; The flameless burning time of each specimen after the second flame is ≤ 60 seconds; Do not allow combustion to spread to the fixture; Allow dripping objects to ignite the cotton pads.
6. Judgment Rules:If only one of the five specimens in a group does not meet all the criteria for a certain grade, the other set of five specimens adjusted for the same condition should be tested. The second group of all specimens shall meet all the criteria specified in this class.
Main influencing factors
The accuracy and reproducibility of vertical combustion test results are restricted by many factors, and the following aspects should be focused on when operating and interpreting the results:
1. Flame Conditions:Flame height and heat output power are the core parameters. The standard requires that the flame height is usually 20mm±2mm, and the flame should be blue in color with its core clearly visible. The stability of gas type, gas purity, flow rate, and pressure directly affects the heat generation and temperature distribution of the flame, which in turn affects the test results. Flame calibration is regularly verified using specialized tools to ensure compliance with standard requirements.
2. Specimen Condition and Preparation:The dimensional accuracy, surface flatness, edge smoothness, and state conditioning conditions of the specimen all affect the combustion behavior. The standard stipulates that the specimen size is usually 130mm±3mm long, 13.0mm±0.3mm, and 3.0mm±0.2mm thick. Specimens are conditioned for 48 hours under standard climatic conditions or subjected to the prescribed aging treatment. The specimen clamping method should ensure that the specimen is vertically flat and avoid twisting or bending.
3. Test Environmental Conditions:The air flow rate in the combustion box had a significant effect on the flame morphology and the combustion of the specimen. The standard requires that the box should have sufficient airtightness to eliminate external airflow interference, and the wind speed in the box should be controlled within the specified range (such as 0.1m/s-0.3m/s). An exhaust device is usually provided on the top of the box to empty the combustion product after the test, but the exhaust system should be closed or adjusted to a position that does not affect the flame during the test.
4. Bunsen Lamp Positioning:The distance between the top of the Bunsen lamp and the lower edge of the specimen is a key positioning parameter, and the standard requirement is 10mm±1mm. For special applications such as automotive interior materials, the gas lamp may be at an angle of 30° to the specimen plane, with a distance of 20mm between the top and the lower edge of the specimen. During the flame application, if the length or position of the specimen changes, the Bunsen lamp should be moved on the vertical plane to maintain the specified relative position.
5. Drip Reception Conditions:The placement, thickness and quality of the cotton layer must meet the requirements of the standard. The cotton layer size is usually 50mm×50mm×6mm, uncompacted, and the mass is about 0.08g. The cotton layer should be dry, and its ignition situation should be accurately judged.
Typical application areas
The application of vertical combustion test chambers has penetrated into several industrial areas where the vertical combustion characteristics of materials need to be evaluated:
Electronic and electrical industry:It is used to evaluate the flame retardant properties of materials such as electrical enclosures, circuit board substrates, connectors, wire and cable jackets, etc. The V-0, V-1, and V-2 grades of UL 94 are the most commonly used flame retardant grading standards in the electronic and electrical industry, which play a decisive role in the safe access of products. In particular, the flame retardant performance of vertically installed electronic equipment components is directly related to whether the flame spreads upwards during a fire and ignites the core components of the equipment.
Automotive Industry:Automotive interior materials such as seat fabrics, dashboards, ceiling linings, wiring harness materials, etc., need to be tested in accordance with GB 32086, 95/28/EC, ECE-R118 and other standards to ensure that the interior materials can self-extinguish or slow down the spread of flames in the event of a vehicle fire. Complex components such as automotive dashboards have vertical surfaces and edges that need to pass combustion tests.
Building Materials:Vertically installed building products such as wall decoration materials, insulation materials, curtains, and pipes need to be evaluated to prevent the flame from spreading rapidly upwards along the wall during a fire.
Polymer material research and production:In the research and development and production quality control of plastics, rubber, foam plastics and other materials, vertical combustion test is an important means to evaluate the flame retardant modification and formulation optimization effect of materials. The vertical combustion test of foam plastics takes into account their apparent density and is determined according to the ISO 845 method.
Textile industry:Vertically hung textile products such as curtains and curtains need to be tested in accordance with textile-specific vertical combustion standards (such as GB/T 5455) to evaluate their flame retardant performance.
Quality supervision and certification inspection:Third-party testing institutions and certification laboratories use vertical combustion test chambers to conduct compliance inspections on various products and provide a basis for product market access.
Selection points to consider
When selecting suitable vertical combustion test equipment for laboratories or quality inspection departments, it is necessary to make a comprehensive judgment based on technical requirements, standards and specifications and practical application scenarios:
1. Tested standards met:Clarifying the test standards that the product needs to meet is the primary basis for selection. Common standards include UL 94, GB/T 2408, IEC 60695-11-10, GB 32086 (automotive interior materials), 95/28/EC, etc. Different standards have different requirements for flame power (50W or 500W), flame angle, flame time, specimen size and state adjustment, and the design of the equipment needs to cover all the requirements of the target standard. Prioritize general-purpose equipment that meets multiple standards and increase flexibility.
2. Flame System and Control Precision:Pay attention to whether the gas control system is equipped with a mass flow meter or a precision flow control valve to accurately control the gas flow and pressure. Whether the flame calibration system is complete, such as thermocouples, flame height gauges and other accessories. The flame height adjustment range (e.g. 10-100mm or 20-175mm) and ease of adjustment meet different standard requirements.
3. Combustion Box Structure and Size:The combustion box should have sufficient internal volume (usually 0.5-1.0 cubic meters) to ensure that the combustion process is not affected by the wall boundary effect. The box should be well sealed to eliminate external airflow interference and equipped with an exhaust system to remove combustion products after testing. The observation window should be large enough and use safety glass to facilitate real-time observation of the test process. The inner wall of the box should be corrosion-resistant for easy flame observation and cleaning and maintenance.
4. Timing System and Automation:The timing device should have sufficient accuracy (0.1s or 0.5s) and the number of channels to record multiple time parameters simultaneously. Automated features such as automatic control of flame application time, automatic trigger timing when specimen is in place, and automatic pause timing of flame burn-out reticles can significantly improve testing efficiency and accuracy. The remote control function increases operational safety.
5. Specimen fixture and positioning mechanism:The specimen clamping device should be able to hold specimens of various thicknesses firmly and ensure that the specimen is vertically flattened. Bunsen lamps should have multi-angle adjustment functions (such as 0°, 20°, 45°) to meet the requirements of different standards. The moving mechanism of the burner and specimen holder should be smoothly adjusted and positioned accurately to facilitate repeated operations.
6. Safety protection features:Since the test involves open flames and combustible gases, the equipment must have complete safety protection measures. It should include gas leakage alarm and automatic cut-off system, over-temperature protection, overload protection, leakage protection and other functions. The exhaust system should be able to effectively remove combustion products and protect the health of the operator.
7. Ease of operation and maintenance:Everyday usage factors such as viewing window lighting, interior cleaning convenience, and gas tank replacement are also worth considering. The digital display and intuitive operator interface help reduce operating errors.